Question
When the Torah mentions a period of days, are they complete or partial days?
Answer
There’s a Talmudic principle that “part of a day is like a day” (Pesachim 4a); this means that part of the first or last day of the period may count as a full day. For example, Noah was told that the Flood would begin in seven days (Gen. 7:4), and it began on the seventh day (7:10). Esther fasted for three days (4:16), and came to the King on the third day (5.1). In Ex.32:1 the people may have expected Moses to return on the 40th day, and lost faith when he didn’t return until the 41st day.